Chemoautotrophs grow by powering CO2 fixation
with the energy released by the oxidation of a
smorgasbord of redox substrates.

Electron donors utilized by these organisms include
reduced sulfur (H2S, S2O3-2, S°, etc.),
reduced iron (e.g., Fe+2, pyrite),
reduced nitrogen (NH3, NO2-)
H2
etc.

O2, NO3-, SO4-2, and Fe+3 (etc.)
can serve as electron acceptors.

 

By coupling the oxidation and reduction of inorganic compounds
to the generation of biomass, the activities of these organisms
tie the geochemical cycle of their redox substrates
to the carbon, nitrogen, and phosphorus cycles.

Further, at H2S, Fe+2, and H2-rich deep-sea hydrothermal vents
and cold seeps, free-living and symbiotic sulfur-oxidizing chemoautotrophs
are dominant primary producers.